Washington residents looked on in dismay Friday as crews finished erecting a metal fence around the Capitol building following deadly riots that saw President Donald Trump supporters raid the famous complex.

The approximately seven-foot-tall fence (about two meters) sealed off the entire Capitol grounds, the scene of Wednesday's extraordinary events that saw hundreds of Trump loyalists ransack the American legislature.

"It's just incredibly sad," a local author who asked not to be named said as he snapped pictures of the black fence that had shuttered the area where he normally enjoys a morning walk.

"The fact that violent protesters decided to overthrow the democratic process. It's a sad week for everyone here."

Five people died as a result of Wednesday's mayhem, including one woman who was shot dead and a Capitol Police officer who was pronounced dead from his injuries Thursday.

While the areas around the Capitol and the White House are typically closed off before an inauguration, two Capitol Police officers told AFP the tall metal fence had been erected in direct response to Wednesday's chaos.

President-elect Joe Biden's inauguration will take place on January 20.

Secretary of the Army Ryan McCarthy has said the "nonscalable" fence would remain for at least 30 days.

Scores of National Guard troops and Capitol Police officers were milling around the Capitol complex, though the area was mostly deserted except for a handful of residents and news crews.

"Our hope is never gone," one Trump supporter yelled at journalists.

The Capitol building is one of Washington's most distinctive structures, known for its gleaming white dome that tops a grand, neoclassical rotunda.